The distribution and abundance of macrobenthos in Jiaozhou Bay during 1991—1995 was compared with that of 1981. Seasonal samples were taken at 10 stations frcn August 1991 to December 1995. Biomass, abundance and biodiversity index were calculated to study the changes during the past 20 years. Cluster analysis and principal component analysis were used to divide the community.rn The species composition changed because some dominant species decreased drastically, such as Raditapes philippinarium and Ternnopleurus toreurnatic. Contrasting to the decrease of large size dominant species, some small size species dominated, such as Heteromastus filiforrnis and Tharyx tesselata. The biomass value, abundance and biodiversity were lower in the early 1990s compared to 1981 and 1995 in inner Bay, but such trend does not exist in outskirts of the Bay. Perhaps such changes indicated that the macrobenthas in Jiaozhou Bay begin to restore after deterioration of enviroment in the late 1980s and early 1990s. The abundance of rnacrobenthos increased significantly; however, the numerical proportion of polychaete, particularly for me small deposit feeders, increased. Such changes could be caused by trawling fisheries, partly because small individuals could avoid direct harms from landing seine, those spedes could reproduce rapidly and they could reproduce all year round.rn The cluster analysis and principal component analysis indicated that the macrobenthic communities can be divided into five groups in contrast to the six communities in 1981. Branchiostoma belcheri is distributed in the 1990s more widely than in the 1980s. The dominant species Ophelina aulogaser in outskirts of the Bay oectwred rarely in the 1990s compared with that of the 1980s. Ruditapes philippinarum was distnbuted in the eastern and western coastal areas in the 1980s. However, we have only recorded once with I individual. Temnopleurus toreurnaticus was a dominant species in the central area of Jiaozhou Bay in the 1980s. However, we have recorded only once with one individual during the five years. The underlying factors for such changes may attribute to trawling fishery. Landing seine can not only hurt target species directly but also do harm to non-target species by destroying the habitat.%采用1991—1995年在胶州湾10个监测站季度取样的资料用聚类和主成分分析法对胶州湾大型底栖生物群落进行分析，并与80年代的资料进行比较。结果表明，一些优势种如菲律宾蛤仔和细雕刻肋海胆等的数量明显减少；90年代初期与80年代相比，湾内的生物量和生物多样性相对较低，到90年代中期又有所回升，而湾内的底栖生物栖息密度却一直呈稳步上升的趋势，尤其是小型底泥食性的种类，如丝异须虫和方格独鳃虫等。主成分分析和聚类分析的结果表明，胶州湾大型底栖生物可以划分为5种类型，而不同于80年代的6种类型，且各群落的优势种变化较明显。导致这种变化的潜在因素可能是对菲律宾蛤仔的过度捕捞。
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